BACKGROUND: The peripheral deafferentation induced by regional anaesthesia (RA) results in misperception of size-shape (S) and posture (P) of the anesthetized limb. During RA, most patients seem to describe motionless 'phantom limbs' fixed in stereotyped illusory positions, suggesting that RA could unmask stable postural patterns. The question of whether movement illusions exist or not after anaesthesia needs a prospective study. This study aimed to describe the phenomenology of RA-induced kinesthetic illusions (K illusions).METHODS: We examined prospectively the body image alteration during infraclavicular blocks in 20 patients. Multimodal sensory testing (pinprick, heat-cold, pallesthesia, and arthrokinesia) and assessment of motor function were performed every 5 min for 60 min after administration of the local anaesthetics. Meanwhile, patients described phantom limb sensations (S, P, and K illusions).RESULTS: We individualized the occurrence of K illusions [44 (8) min] with respect to S illusions [7 (3) min; P<0.005] and P illusions [22 (4) min; P<0.001]. A close relationship between the onset of K illusions and proprioceptive impairment (arthrokinesia: r=0.92, P<0.001; pallesthesia: r=0.89, P<0001) and abolishment of motor activity (r=0.83, P<0.001) was identified. Finally, a principal component analysis showed that S and P illusions were essentially related to the proprioceptive impairment.CONCLUSIONS: This study analyses for the first time the temporal evolution of sensorimotor dysfunction and the onset of K illusions during RA. Our results suggest the involvement of an alteration of proprioception and motor functions in the origin of this phenomenon. These data agree with the motor awareness theory.